Low voltage oscillatory circuit



ATTORNEYS Sept. 2, 1958 c. E. ATKINS v 7 LOW VOLTAGE OSCILLATORY CIRCUITFiled NOV. 23, 1955 United States Patent LOW VDLTAGE OSCELL ATQRYCIRCUIT Carl E. Atkins, Bloomfield, N. .l., assignor to Tong-SolElectric the, a corporation of Delaware Application November 23, 1955,Serial No. 548,681 Claims. (Cl. 317-130).

The .present invention relates to anovel low voltage oscillatory circuitsuitable for use as a multivibrator and to a light responsive circuitincorporating the new oscillatory circuit.

' As the. new oscillatory circuit, while of general application, isparticularly adapted for. use in the control of automobilelheadlamps inresponse to incidence of light, it willbe described with reference tosuch application and particularly-with reference to the type of lightresponsive system disclosed and claimed in my prior pending applicationsSerial No. 433,959, filed June 2, 1954,

arid-Serial No. 547,508, filed November 17, 1955, over photoelectrictube and a relay control tube connected to the oscillatory circuit toreceive controlling pulses therefrom when the photoelectric tube issubjctedto light, the relay controhtube being normally conducting tohold energized in its plate circuit a sensitive relay which, uponreleasev of 'its armature, closes contacts controllingthe circuit of apower relay. Five electronic tubes, or tube sections where double tubesare employed, are required in addition to the photoelectric tube, ineach of the circuitsof my said prior applications. These five comprisethe electrometer tube or tube section, the phase inverting tube. ortubesection, two tube sections of a 'double triode connected as amultivibrator and the relay control tube.-

In the new light responsive circuit incorporatingthe novel-oscillatorycircuit of the present invention only three -.elect-ronic tubes or tubesections are required as contrasted to the five required in my priorcircuits. The need for a phase inverter tube section has been obviatedand the-relay control tube serves not only to control the sensitiverelay but'also as one of the two tubes of the new oscillatory circuit.

In the. new oscillatory circuit, unlike the usual multivi-brator'circuit, oscillations areinitiated by application of negative potentialto the control grid of the first of the two tubes or tube sections andquenched by application ofpositive potential to such grid. Hence in thelight responsive circuit, the potential of the anode of theelectrorneter tube which decreases with increase in intensity of lightincident on the photocathode' and increases when the intensity of theincident light decreases, can'be used directlyasthe control potential ofthe oscillatory circuit toqinitiate oscillation thereof when light of apredetermined intensity is incident. on the photocathode and to quenchthe oscillation of the oscillatory circuit when the intensity ofincident light reduces to a predetermined value.

i at ented Sept. 2,

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the circuit to thecontrol of the dimming switch ofan automobile theinductor is the sensitive relay hereinbefore mentioned in connectionwith the description of the. circuits of the said prior applications andthe source .of voltage is the car carried battery of nominally 12 volts.When the oscillatory circuit is quiescentthe control grid potential ofthefirst tube is such that the tubepas ses maximum current and hence anyincrease in positive potential applied to the control grid can notincrease the anode current. A decrease. in control grid potential will,however, reduce the current through this tube and cause an increase inpotential at the anode thereof. The anodes and control grids of the twotubes of the oscillatory circuit are so interconnected that increase inpotential at the anode of the firsttube will initiate oscillations ofthe circuit. Oscillations will cease when the control grid of the'firsttube is raised sufficiently to cause'the. tube to a a n ec m s t r teBre ferably. the second tube of the oscillatory circuit, the relaycontrol tube, is ofthe space charge grid type, the first gridbeingrnaintained at a positive potential of say 8 volts and the secondgrid servingas the control grid. Alarge bias resistor isprovidedfor-thecontrol grid to cause the potential of the grid to be drivennegative by the self-rectifying properties of the grid cathode circuitwhen positive pulses from the anodeof the'first tube are impressed upon.the control grid of the second tube. Thus during oscillation of thesteady current through the second tube is gradually reduced to releasethe sensitive relay whereas pulses of relatively large magnitude due tothe inductive eifect ofthe relay winding appear at the anode. of thesecond tube to be transmitted back to. the

control grid of the first tube to maintain'the circuit in oscillation.

For a better understanding of the oscillatory circuit and of the newlight responsive circuit incorporating the same reference may be had tothe accompanying drawing 0 which:

Fig. 1 is a circuit diagram of a light responsive circuit embodying theinvention;

Fig. 2'is a graph explanatory of the operation of the first tube of theoscillatory circuit; and

Fig. 3 is a'diagram illustrating an alternative arrangement for part ofthe circuit of Fig. 1.'

In. Fig. -l the light responsive circuit of the invention is shown asincluding a double tetrode 2 the first half 2a of whichoperates as theelectrometer portion of the circuit .mand the second half 2b of whichoperates as the first tube of the oscillatory circuit, and. a relaycontrol tube 4 whichserves also as the second tubeof the oscillatorycircuit. The control grid 6'of'the electrometer portion 2a oftube 2 isconnected to the photocath'ode' of 'a photoelectric tube 8, the anode ofwhich is grounded. The cathode 10 of the electrometer portion 2a isgrounded and the screen grid 12 and anode 14 thereof,'are connectedthrough respective dropping resistors 16 and 18 to a line 20 maintainedat a regulated voltage of 8 volts. Resistor 18, as indicated in Fig. 1,is made adjustable to serve as the hold control. The screen grid 12 isalso connected through an adjustable resistor 22, comprising the dimcontrol, to a front contact associated with the grounded armature 24 ofthe sensitive relay 26 in the anode circuit of tube 4.-

Anode 149of section 2a is connected through a resistor 28 to the controlgrid 30 of section 217. The cathode of the operating point at whichsaturation occurs.

order of 15 milliamperes. gized holding open the circuit of the powerrelay 54 at the section 2b is operated at above ground potential byvirtue of a connection to the junction of a pair of resistors 32 and 34connected in series between the 8 volt line 20 and ground. The 8 voltline 20 is connected directly to the screen grid of section 2b and,through a dropping resistor 36 to the anode 38 of that section.

Anode 38 of section 211 is also connected through a capacitor 40 to thesecond or control grid 42 of the output tube 4. The control grid 30 ofsection 211 is connected through a capacitor 44 to the junction betweena resistor 46 and capacitor 48 series connected between the anode 50 oftube 4 and ground. The circuit comprising resistor 46 and capacitor 48serves as a potential divider and phase shifter for pulses fed back fromanode 50 to grid 30.

The cathode of tube 4 is grounded and the first or space charge gridthereof is connected directly to the 8 volt line 20. A grid biasresistor 52 of relatively large magnitude, say two megohms, is connectedbetween the grid 42 and ground. A car carried battery (not shown) of theorder of 12 or 13 volts is connected to the anode 50 through the relay26 and is, connected through the winding of a power relay 54 to the backcontact associated with armature 24 of relay 26.

Any suitable means, as for example, a gas filled regulator tube ofconventional construction may be employed for obtaining from the batterythe regulated 8 volts for application to line 20. Such means have notbeen shown because forming no part of the present invention and becauseadequately disclosed in the pending applications to which reference hasalready been made.

The operation of the circuit of Fig. 1 will now be given with referenceto that figure and also with reference to the graph of Fig. 2. Underconditions of low or no light on the photocathode of the photoelectrictube 8 electrons from the heated cathode of the electrometer portion oftube 2 will accumulate on the grid6 and drive that grid suflicientlynegative to maintain relatively low current through the electrometerportion 2a of the tube.

When dropping resistor 18 is of say 100 K and resistor 28 of about 300 Kthen the potential at the anode 14 -will be relatively high say 2 voltsor higher and the potential of grid 30 will be at least about one andone-half volts above ground, or Zero with respect to the cathode.

Accordingly section 2b of tube 2 will be in its most conductivecondition. The value of resistor 28 is so chosen that the potential ofgrid 30 under such conditions of low current through the electrometerportion 2a will be high enough to insure that the current through thesecond half of tube 2 is that corresponding to saturation at theoperating voltages. In Fig. 2 wherein plate potential above ground isplotted against grid potential above cathode potential a grid voltage ofzero volts corresponds to Increase in positive potential of the gridbeyond this value can not change the anode potential because the anodeis already taking all the current it can draw. Decrease in gridpotential below this operating point will however, reduce the currentthrough the section 2b and thereby result in increase in anodepotential.

Still assuming the no or low light conditions, the tube 4 will beconducting and will pass a steady current of the Accordingly relay 26isenerback contact of armature 24 and holding closed the circuit throughthe dim control 22 to the screen grid 12 of the electrometer portion 2aof tube 2. No oscillation of the circuit including the second half oftube 2 and the tive charge accumulated by control grid 6 will dissipatethrough the photoelectric tube thereby raising the potential of grid 6and causing increased current to flow through the electrometer portion2a. The potential at anode 14 therefore decreases and that at grid 30likewise decreases. When the potential at grid 30 is sufiiciently belowthe operating point (zero with respect to the cathode), the currentthrough section 2b will decrease raising the potential at anode 38 andapplying a positive pulse through condenser 40 to control grid 42 oftube 4. This will result in a momentary increase in current through tube4 which increase is reflected as a drop in potential at anode 5t) and,through the phase shifting and potential dividing circuit comprisingresistor 46 and capacitor 48, as a negative pulse applied to grid 30.This negative pulse on grid 30 causes a positive pulse to appear atanode 38 and at control grid 42 which in turn reinforces the negativepulse at anode 50. When tube section 2b reaches cut off, the potentialat anode 38 can rise no further. Consequently when the pulse appliedthrough condenser 44 dissipates, the anode potential falls and thereverse cycle is initiated. Thus the oscillatory circuit comprising thesection 2b and the relay control tube 4 will break into oscillation andcontinue to oscillate so long as the current through the electrometerportion 2a is sufi'icient to maintain the grid .30 at an averagepotential below that of the operating point indicated in Fig. 2.

Because of the presence of the inductive winding of the sensitive relayin the anode circuit of tube 4 the pulses created at anode 50 will bestrongly negatively peaked and of a magnitude more than suflicient tomaintain the circuit in oscillation. The steady current through tube 4which is effective to hold the relay energized will gradually decreaseduring oscillation of the system due partly to the decrease in theaverage potential of grid 42 resulting from the self-rectifyingproperties of the grid circuit including the high resistor 52 andcapacitor 40 and to the fact that the inductive kick drives the anodepotential so low during positive excursions of the grid voltage thataverage plate current is reduced.

The potential dividing circuit comprising resistor 46 and capacitor 48serves to reduce the magnitude of the pulses applied from anode 50through capacitor 44 to control grid 30 and at the same time to shiftthe phase of these pulses to insure that oscillation will be continuedso long as a light signal is present.

When the relay 26 releases the circuit of the power relay 54 is closedthrough armature 24 and the dimming switch (not shown) will be actuated.The circuit through adjustable resistor 22 is opened at the frontcontact of armature 24 and consequently the potential of the screen grid12 of the electrometer portion of tube 2 is increased to increase thesensitivity of the circuit and to thereby insure that dimming of thelights of an approaching car will not cause return of the circuit tohigh beam conditions.

The control grid 6 of the electrometer portion 2a is preferably takenout through a top cap as indicated diagrammatically in Fig. l by thebracket 56. Preferably also this portion of the double tube 2 is of theconstruction illustrated and described in my said copending applicationSerial No. 547,508 filed November 17, 1955, which construction insuresthat change in cathode emission will not appreciably affect anodecurrent. The construction involves a grid pitch-grid cathode spacingratio less than unity to avoid island formation as explained more fullyin said copending application.

Also the internal lead from grid 6 to the top cap is preferably sodisposed with respect to the anode 38 of section 2b that there will be acapacitative coupling between that anode and grid 6 and the partsconductively connected thereto such as the top cap 56. Such coupling, ofthe order of 0.1 micromicrofarad, which is symbolized in Fig. l by thecondenser 58 shown in dotted lines, serves to increase the speed ofresponse of the circuit to change in light intensity, as explained inthe said copending application. When the negative charge on grid light,and current through section 2b consequently reduces, the increase inpotential at anode 38, through its capacitativecoupling to grid 6,causes the potential of that grid to rise more quickly and henceaccelerates the response of the circuit.

In the construction of double tetrode described in the said copendingapplication the heaters are provided with unequal thickness ofinsulation to insure that the first half of the tube will heat up morepromptly and thereby insure that when the circuit is first put intooperation the dimming switch will be operated irrespective of lightintensity. In the present circuit this result is automatically obtainedduring the. charging. of grid 6 from the cathode. Hence unequal rate ofheating of the sections of the double tube is unnecessary and undesired.Both heaters are therefore preferably fast acting.

In thecircuit of Fig. 1 the control grid 30. of tube section 2b isconnected both to anode 14 to receive control potential therefrom andthrough capacitor 44 to the potential dividing and phaseshifting..network to receive pulses therefrom during a light signal. Analternative .arrangement, wherein the feedback pulses are applied to thescreen grid, rather than to the control grid of tube section 2b isillustrated in Fig. 3.

In Fig. 3, control grid 30 of section 2b is shown connected only toanode 14 of the electrometer section 2a and the screen grid 60 is shownconnected to capacitor 44. The resistor between anode 14 and grid 30 isomitted and a potential dropping resistor 62 is included in theconnection between the 8 volt line 20 and grid 60. The remainder of thecircuit, being identical with that of Fig. l, is not shown in Fig. 3.The operation of the circuit of Fig. 3 does not differ in any materialrespect from that described with reference to Fig. l. The feedbackconnection to the screen grid rather than to the control grid has theeffect, however, of keeping oscillatory current out of the droppingresistor in the anode circuit of the electrometer portion of tube 2.

An illustrative set of specific values of the several electricalcomponents of the new system are given in the following table.Electrical components having values different from those given in thetable could be employed in a system operating in accordance with theinvention, as will be obvious to those skilled in the art.

Table of illustrative values of circuit components R16 680 ohms.

R18 100 kilohms--variable. R22 kilohms.

R28 300 kilohms. R32 5 kilohms.

R34 1 kilohm.

R36 100 kilohms. R46 22 kilohms.

R52 2.2 megohms. C40 .002 microfarad. C44 .001 microfarad. C48 .0005microfarad.

Capacitative coupling 58 about .01 micromicrofarad.

The invention has now been described with specific reference to controlof the dimming switch of automobile headlights in response to incidentlight. Obviously the utility of the new oscillatory circuit of theinvention is not limited to such specific application.

The following is claimed:

1. An oscillatory circuit comprising a first and second electronic tubesection each having an anode and a cathode and at least one grid, meanscapacitatively coupling the anode of each section with a grid of theother section, a first conductive impedance, means for impressing apotential difference across said impedance and said first section inseries, grid biasing means for said first section, a second conductiveimpedance, means for impressing a potential difference across saidsecond impedance and second tube section in series, said secondimpedance be ing of a magnitude selected with reference to the magnitudeof the potential difference impressed across said second impedance andsaid second tube section and with reference to the characteristics ofsuch tube section as to cause such section to be current saturated whenthe potential of a grid thereof with respect to the .cathode thereof-isat or above a predetermined value, and means for initiating oscillationof the circuit by depressing the potential of said last mentioned gridbelow said predejtermined value and for quenching oscillation of saidcircuit by raising the potential of said last mentioned grid above saidpredetermined value, said last mentioned means comprising a separateenergized circuit connected to said last mentioned grid and to thecathode of said second section and having meanstherein for varying thepotential of said last mentioned grid.

2.'The oscillatory circuit according to claim 1 wherein said firstconductive impedance isan inductive impedance whereby during oscillationof said-circuit the average current through said first tube sectiondecreases.

3. The oscillatory circuit according to claim 2 including a resistor andcapacitor connected in series across said first tube section to serve asa potential dividing and phase shifting network for pulses fed back to agrid of said second tube section, said means capacitatively couplingsaid last mentioned grid of said second tube section to the anode ofsaid first tube section comprising a capacitor connected between saidgrid and the junction of the resistor and capacitor of said network.

4. The oscillatory circuit according to claim 3 wherein said inductiveimpedance comprises the winding of a sensitive relay energized by thesteady current through said first tube section when the circuit is notoscillating and wherein said grid biasing means comprises a high biasresistor connected between the cathode and the grid of said first tubesection that receives pulses from said second tube section when thecircuit is oscillating, whereby during oscillation of the circuit theaverage current through said first tube section and relay windingdecreases to release the relay because the grid is driven negative byvirtue of the self-rectifying properties of the cathode grid circuitincluding said bias resistor and because the inductive kicks at theanode depress the anode potential during parts of the time that positivepulses are impressed upon the grid.

5. The oscillatory circuit according to claim 1 wherein said secondconductive impedance comprises two resistors one connected to the anodeof said second tube section and the other connected to the cathode ofsaid second tube section and wherein said separate energized circuitcomprises a third electronic tube section, a dropping resistor, meansfor impressing a potential difference across said dropping resistor andthird electronic tube section in series, and a connection between a gridof said second tube section and the junction of said third tube sectionwith said dropping resistor whereby the potential applied to the grid ofsaid second tube section varies with the current through said third tubesection.

6. The oscillatory circuit according to claim 5 including a resistor insaid connection to reduce grid current of said second tube section andto minimize oscillatory current in the dropping resistor connected tothe third tube section.

7. The oscillatory circuit according to claim 1 wherein said second tubesection has both a control grid and a screen grid, said control gridbeing connected to said separate energized circuit and coupled to thefirst tube section for reception of voltage pulses therefrom when thecircuit is oscillating, said screen grid being connected for operationat constant positive potential.

8. The oscillatory circuit according to claim 7 wherein said separateenergized circuit comprises a thirdelectronie tube section and droppingresistor, means for impressing a potential difference across said thirdelectronic tube '7 section and dropping resistor in series and aresistor connected between the control grid of said second tube sectionand the junction of said third tube section with its dropping resistor.

9. The oscillatory circuit according to claim 1 wherein said second tubesection has both a control grid and a screen grid, said control gridbeing connected to said separate energized circuit and said screen gridbeing connected through a dropping resistor to said means for impressinga potential diflerence across said second impedance and second tubesection in series and being coupled to said first tube section forreception of voltage pulses therefrom when the circuit is oscillating.

10. The oscillatory circuit according to claim 1 wherein said secondimpedance comprises a dropping resistor connected to the anode of saidsecond tube section and a cathode resistor connected to the cathode ofsaid second tube section and wherein said separate energized circuitincludes a third electronic tube section having a cathode, at least onegrid and an anode, a third conductive impedance, means for impressing a.potential difference across said third impedance and said third tubesection in series and a connection between the anode of said third tubesection and the grid of said second tube section, said second and thirdtube sections having a common envelope provided with a topcap to whichthe grid of said third tube section is internally connected, theelectrodes Within said common envelope being so oriented and theinternal connection to the top cap being so disposed that there will bean inherent small capacitative coupling between the anode of said secondtube section and the grid of the third tube section which acceleratesresponse of the circuit to change in potential of the grid of the thirdtube section.

References Cited in the file of this patent UNITED STATES PATENTS2,659,008 Floyd Nov. 10, 1953 2,682,026 Mesh et al. June 22, 19552,735,009 Harry Feb. 14, 1956 2,773,219 Aron Dec. 4, 1956 2,773,220 AronDec. 4, 1956 2,777,097 Atkins Jan. 8, 1957

